The present invention relates to a force imparting device and/or capacitor displacement sensor and more particularly to a multi-plate capacitive transducer.
Capacitive transducers have wide application, including use as pressure and displacement sensors, accelerometers, and micro indentation or micro hardness testing devices. Capacitive transducers offer several advantages, including high sensitivity and resolution. A multi-plate capacitive transducer with two layers of springs provides for parallel motion of the shared pick-up plate with respect to the upper and lower drive plates. Parallel motion is known to stabilize the total gap between the drive plates and the shared pick-up plate. Prior art devices of this configuration have included a separate spacer member to separate the drive plate and pick-up plate electrodes, which increases the complexity of assembly and the number of plates that must be bonded by adhesive, generally an epoxy. Some of the materials used in prior art devices, including the epoxy, can be sensitive to temperature and moisture, limiting the effectiveness of the sensor and/or lifetime of the device. The pick-up plates, which include the springs, are generally of a single thickness determined by the desired spring constant. Pick-up plates having a single thickness create a spring geometry more sensitive to deformation. Additionally, metal pick-up plates of the prior art devices have been manufactured from commercially available shim stock with relatively high manufacturing tolerances and spring stiffness variation.
A need exists for a multi-plate capacitive transducer with parallel motion that eliminates the use of epoxy adhesives, reduces the number of interfaces to simplify assembly, allows for improved manufacturing tolerances, is less susceptible to changes in humidity and temperature, and comprises springs that are less sensitive to unintended deformation.